If you’re typing "forego," you may get questioned by your computer to see whether you meant “forgo” — that’s how similar these two words are.
So if you’re confused about the difference, hopefully remembering this will help: When you add the “e” it means something that precedes you. When you drop it for forgo, you are passing up the chance to use that extra vowel, which happens to be the general meaning of the word — to go without.
Forego basically means something that has come before — to proceed.
Forgo means something that was missed and passed up.
But, like so much of the ever-changing English language, these two differences have been relatively lost over time. But, hey, if you want to impress a nerd in a word fight, consider differentiating them.
You’ll probably win points, but it’s not a foregone conclusion.