I've been at this since the eighties and, in addition, was raised in an investment family (just like there are mechanic families and real estate families, there are families where talk about investment is the main topic).
I say buy good stuff and hold it. Review everything a few times a year, rebalance if you choose, get rid of your mistakes -- but mostly hold on. Keep a long time horizon, years not months or weeks. Diversify like crazy to spread out the risk. I know it's boring, but low cost mutual funds focused on the broader market (like, not a tech fund for example) do that for you very affordably.
If you like the games aspect of investing, set aside a sum you can afford to lose and go for it. Keep your retirement fund separate and don't mess with it.
For people who want to be aggressive, there's nothing I can say to dissuade you and you know the risks. If you're willing to accept the potential of losing a whole lot as well as gaining a whole lot, I think that's almost a fixed personality trait and people born with it have to work out their own strategies for living with the results.
I'm old now and I'm really glad I did what I did. If you don't care, or if you have kids who hopefully can bail you out twenty or more years from now if things go south, that's a whole different story.
Incidentally, I do have some Apple and watched the same drop everybody else did. I never look at it as a loss. A loss is when it's realized (that is, you sell), not all the fluctuations along the way. That's crazy making. You still have X dollars in Apple, and on any day you can ask yourself, with expenses and tax issues taken into account, it'd be better off staying in Apple or being put somewhere else.
But not better off two days from now. Better off in two, or five, or ten years.
The data show most people who try to time the market do not, over time, outperform the market.