The perfect circumstances do not exist, so stop waiting for them.
You will never feel completely ready or completely fearless. There will always be reasons to stay in your comfort zone. But if you want to change careers, work on recurring destructive behaviour patterns, adopt a healthier lifestyle, amend or quit a relationship, become grateful, enjoy a simpler life... start in the HERE and NOW. There's no better place and no better time than NOW.
If not NOW then WHEN?