Since i've been freelance basically for 20 years in some capacity or another, I would say my lesson is that network IS net worth and, quite honestly, it's more about how many people you know to keep you in work and finding clients.
sadly, this has always been my worst skill, I just like hunkering down and doing the job without all the social bollocks and networking, I'm definitely worse off for it though!
what wisdom have your jobs taught you?