I interpret this directly as: don’t ever put yourself in the position where you might regret the things you didn’t do,
which leads me indirectly to: don’t hold back from doing the things you could have done because you’re likely to regret it later.
The word adventure didn’t spring to mind when I read your post (though I get what you mean). Holding back from the things you could have done could be interpreted as just about anything, but it depends on context. Examples: you could have sent a letter; you could have taken a job; you could have helped a person in need. Or, it could be something more adventurous as: you could have taken that road trip; could have asked that person out on a date. In all instances, having taken the plunge, where might things have led had you said yes?
Go now, go now, don’t hesitate, your only master’s you,
Don’t ever let yourself regret the things you didn’t do
have great clarity. Fab!