You didn't lose the game, you just decided not to play for the past several years. However you still probably have a few decades of life ahead of you. The new game starts today. How you play is up to you. Educate yourself about how a bear market is not the end of the world when you're playing the long game and you might be more confident. However I stand by what I said earlier: you need to pick an asset allocation that you're comfortable sticking with through a bear market. Maybe 80/20 is not that allocation for you. The fact that you are concerned about investing a lump sum says that this might be the case.
I am not concerned about investing the lump sum. My main concern is entering the market with basically most of the net worth at the possible peak. I know you cannot time the market, but given all the hype about a major correction the media now - it is not the most comfortable time for me to enter. On the other hand, usually when most people expect a significant collapse, it does not happen.
When you're already in the market, each day you don't sell you're making an implicit decision that things are likely to go up from here. What if you had invested a year ago? Would the doomsday articles cause you enough concern to pull your money out today?
No, if I am already in, I wouldn't sell. It was my mistake not to enter due to my ignorance and lack of understanding... However, almost everyone is now screaming that the market is about to collapse - everything is overvalued, economy is not doing great, major correction is coming, etc.. It is mentally tough to enter the market, especially after missing on such an amazing bull run.
There are lots of people screaming about a crash, but they apparently aren't putting their money where their mouth is. The market is this high because when people think it's worth it when they actually go to pull out their wallet. That doesn't mean we're not in a bubble, but ask yourself if you think you're smarter than millions of talented people put together.
I personally think the market is way high but there are several reasons that it doesn't matter:
a) I could be completely wrong.
b) Most other things you can invest in right now are doing pretty pitifully. You're getting almost no interest on your cash for instance.
c) There are scenarios in which the market could correct itself without a crash.
d) Major companies are nervously sitting on huge piles of cash right now just like you. That cash is part of a company's value as much as their earnings. Also, when they overcome their fears and invest, the market might very well take off.
e) If you're in it for the long term, today's valuations aren't really that important.
f) Don't forget the basic idea that you're buying pieces of companies. Those companies are churning out profits every day, and every day you wait is a day you're missing out on that.