A significant drop was bound to happen. I can't speak for others, but that drop only sliced 1/3 or less off the gains I've seen SINCE New Years. Give me 12 months of that performance and I'll be retiring much earlier than I expected.
I'm 52 and I've seen 3 big bust already in my life. When it comes, it's hurts like ****, but investing in the stock market has to always be for long term, regardless of how often you might trade.
My humble advice: Save young & consistently fund your retirement plans without regard to the curernt market. Pay attention but be patient. Always keep near term cash needs out of the stock market.
10 years can be a lifetime to someone in their 20-30s, but the market will inevitably recover, often quite faster than anyone anticipates.
So many people panic and sell or quit funding their 401ks in a down market and miss the rebound that makes a difference. On the contrary, I'm hesitant to continue buying "high" at the current market - but you leave your 401K on auto-pilot.
That being said:
Generically, the technology funds are the the future and I can only see that escalating in this age. I have varying stocks, but saw the value in Amazon years ago. Hadn't been to the mall since

.
I personally am a believer in energy funds but you have to get burned a few times to fully understand the ebb and flow of gas & oil.
Fracking technology has been so wildly successful that the US is again the #1 produceer - unfathomable just a decade ago. The Saudis lost market share, got clever and decided to intentionly flood the market sending oil stocks down as much as 90% in some cases. The Saudis made a grave error and after years had to cap production with OPEC. Oil & Gas are not going away my friends and that was a buying opportunity for me.
Obviously these pose more risk, but my personal favs are the sand stocks, ie US Silica, FMSA. The beauty is that in the slowdown - copanies learned to improve their processes to make fracking more efficient. Turns out that more sand in the process produces more yield. These guys have rebounded already but I think will ultimately double again as oil returns above 50-60/barrell. It's just a matter of time.