It’s a common thing to say when arranging meetings at work, e.g.: “When works for you? I’m flexible.” But it equally applies to organising things with your friends and family.
You probably say “I’m flexible” out of consideration for the other person, allowing them to pick a convenient time.
Despite the good intentions, saying “I’m flexible” has the opposite effect – it’s not really considerate. It is passing the ‘cognitive buck’. You’re asking the other person to handle the scheduling problem.
Studies show that people are more likely to accept a meeting request when you propose a specific time and date (e.g. Tuesday at 2:00pm), compared to leaving it up to them. We prefer ‘constrained’ decisions, especially when we’re busy.
Of course, you should remain prepared to be flexible when requesting someone’s time, even if you don’t say it. Propose a time (bonus points if you actually give some thought to what might work best for them), and then be flexible if they come back with an alternative.
It’s an old habit for me. But moving forward I’ll try to be kinder and stop saying “I’m flexible”.