An ambition can be serious without occupying every conversation you enter.

Talking about an ambition can substitute for pursuing it. Describing the plan produces some of the same satisfaction as progress, and the enthusiasm is easier to renew than the work, so the subject keeps arriving in conversations that were about something else. It also flattens you into one topic for the people around you, who came for company rather than an update.

Let one conversation go by without mentioning the thing you are working toward. Ask about the other person instead. Keeping some of it unspoken tends to leave more of it available for the actual work.