That’s a great set up, I’ve been chatting about this with a couple of people recently 
TL;DR
This is consistent with a J.P. Morgan Asset Management report published in 2016, “Staying Invested During Volatile Markets,” which found that around 60% of the biggest single-day percentage gains in the S&P 500 occurred within two weeks of one of its top-10 largest percentage declines between 1995 and 2014. This means even if you’re lucky enough to hit the nail on the head once in a while, no one has the foresight to correctly predict every major pop and plunge in these major indexes with any consistency.
If you miss even a small handful of these major moves higher, you can kiss a good portion of your long-term return goodbye. According to J.P. Morgan Asset Management’s report, for the 20-year period between Jan. 3, 1995 and Dec. 31, 2014 (including both the dot-com bubble and Great Recession) the S&P 500 returned 555% (9.9% annualized) for those investors who held on and never sold. If you missed just the 10 best days in terms of percentage gains over this more than 5,000-day period, your return was more than halved to 191%.
quote from: This Is Precisely Why Timing the Market Isn’t Worth Your While
Whenever you first invest, time is on your side. Over the long haul, the compounding returns of a well-chosen investment will add up nicely, whatever the market happens to be doing when you buy your first shares.
quote from: When’s the Right Time to Invest?
There’s some important caveats to bear in mind from those articles so please do read the whole thing. But that’s basically my mentality when it comes to investing.
Bear markets aren’t fun but (last quote 
)
What you need to know about corrections:
- They’re a 10-20% fall in the stock market
- They happen once a year on average
- The average fall is 13.5%
- And the average duration is 54 days
What you need to know about a crash (also called a bear market):
- They’re a stock market fall of more than 20%
- They happen on average once every four years
- The average fall is 33%
- And the average duration is one year
Don’t forget, 80% of corrections do not turn into crashes. And so far, 100% of crashes have been followed by a recovery that more than recovers the fall.
quote from: Is the stock market risky?