What do you wish you knew before trying entrepreneurship?

Been flirting with/ trying to identify the potential market for a product idea for the better part of a year, and I'm going to go for it and start prototyping and developing my go to market strategy over the coming months, maybe even get a finished product out this year.

For all of you out there who have tried the entrepreneurship life, successful or not, what is the one lesson you wish you had learned earlier in your journey/ career? Any key pieces of advice for the wide-eyed youths?