I wish I knew.
My company started deducting my pay for my 401k payments. Then, one day, the boss announced that there weren't enough people participating, so they were quitting the deduction plan. If the employees wanted to continue contributing they could do it themselves. I didn't make any more payments but I thought the money that I had already invested would at least still be in my account accruing interest. It wasn't a huge amount but it was a nice little extra for my retirement some day.
Then I decided maybe I should move it into an account that I could monitor better. When I checked on my balance, it was zero! The reason stated was that my account was no longer vested, so it just drained out.
If I had known that that would happen, I would have taken my money out a long time ago. But now it's too late.
It was a big waste of my money. I got absolutely nothing for it. I could have done better just putting it in the bank.