Parabolic thrusts, almost always evoke contradictory moods among investors, for any stock (or Index) involved, especially when it's on-top of historically lengthy runs.  

You have professional investors rationalizing upside extensions (which generally will require revenue to actually meet or beat rosy expectations), and bears consistently in an argumentative mode, as to 'why' a stock or Index 'can't go higher', though it does. 

We have not made that argument, and since calling the March low (to the day) have cautioned against aggressive shorting or fading of the S&P because of: both the Fed stance (TINA), and money managers who missed our low staying in catch-up mode (of course that's referred to as FOMO).  

That is where the market is now, whether it's Apple (AAPL), Tesla (TSLA) or the NDX (NDX) itself. It's not exactly the case for S&P, although the compression of total capitalization both lifts the Index, but concentrates 'control' of the Index into just a few issues, as you know.

Sectors are bifurcated and in a sense strong. And it will persist overall, shakeout or not if a coupe things happen, and there lies the rub: the current pandemic controlled life-changes, require a focus on homes and schools, and online communication. So stocks in these areas (housing and connectivity besides direct beneficiaries in tech and telecom of course) dominate the action, aside the wild oscillations of biotech as the Nation and the world crave definitive news that might shuffle the players within a presumed 'new normal' that inevitably follows.  

That could be more old normal life than they think, 'if' we get an effective therapeutic, such as a pill, with would dramatically relegate Covid to an entirely ratcheted-down level of concern). But so for that's all aspirational. But it is why investors can (as most probably should) avoid the insane gyrations of a number of pharma / biotech players, by just staying parked in reliably-dividend playing stocks, or outside of the direct area of action, which centers along the highly combative arena of scientific progress.  

As it became a bit politicized (to say the least), and investors recognized the bulk of a great deal of funding went to either biggest pharmas or leading players (we would not say biggest donors to political causes or even learned medical entities), who did earn a 'shot' at first-mover advantage, but none have come-through impressively. In my conversations and the reports I've perused, there is not 'yet' the testing efficiency or even hospital care treatments that pass the term of being call 'reliable'.  

That's too bad, because the world needs this to be resolved. And besides stocks (for those who wish to dance amid the minefield of speculative plays with a few bucks as I haven't seen that as a safe area for significant investment at any time), the return of everything from airlines to restaurants (beyond basic) to caring about 'style' relates a great deal to citizens feeling 'comfortable' working, mingling and socializing publicly.

In-sum: we'll get to a sort of normalcy, and I just wanted to share how it might shift a slew of sectors, while actually reinforcing upside in some that are already expensive.  

The shifting of Dow components comes at an interesting time, and is presented as a sign that the world's changed, and energy is less important.. for investors too. That's the signal DJ is sending to the market, and it's a bit premature but recognizes trends that Covid (besides global warming) has brought to greater understanding. However the U.S. 'energy independence' matters, and while multiples won't return to 'old days' levels, energy does matter (at least my decades-favorite Chevron (CVX) is still aboard).  

I don't think energy is the story of the moment, but I do suspect Oil will be stronger in the immediate years ahead than people anticipate, though lower equity multiples. Of course it's not time to establish new oil investments but speaking as someone with a few long-term shares in Oil (and tiny actual well royalties), I'm not inclined to sell.  

I suppose the real question is would I sell an Apple or a Tesla or any parabolic runs, and the answer is different, and depends on competitive situations more for the latter than the former, and again not yet. But a heavy investor could hedge positions with a few strategies to avoid a tax event (a little earlier than usual) while locking-in gains. I suspect large investors with such stocks in tax-deferred retirement accounts might sell a bit from time-to-time, while regular accounts might write covered options very carefully, to enhance income while hoping to retain the underlying securities.  

All that varies greatly between investors (or traders) that I rarely delve into this arena. As to energy the world still runs on oil, we are 'sort of' re-suburbanizing residency in the suburbs and even small communities where drive-times are greater than before. For oil (OIL), you're past a cyclical low I noted earlier this year, believing Crude bottomed and we'd move somewhat higher as we did. I expect surprisingly high oil in 2021.  

Bottom-line: the uptrend of the NDX and S&P (SPX) isn't ironclad, but actually enhanced by a perpetuation of this convoluted economy, but it requires funding that isn't visible. Hence the 'sustainability' of this pattern is in-question, while Covid does show sector shifts (I touched only on a couple), and if you want a bullish case for the S&P, that's going to be Oil and Banks (who are owed a lot of money by many oil companies), so it is just the ticket to sustain the overall 'market structure' during the pandemic, if we can migrate to the illusive therapeutic drug treatment before a wider collapse.