Clients often tell me they will speak up in meetings once they feel more confident. In my experience it works the other way round. Confidence follows action, rarely the reverse.
Build an evidence file
Keep a simple note of things you handled well: a tricky email, a meeting you led, feedback you received. On a hard day, read it. It is much harder to argue with a list of facts than with a vague feeling.
Make the first step smaller
If presenting to the whole team feels too much, start by asking one question in a meeting this week. Then two. Small repetitions add up faster than you expect.
