It depends whether someone is making a reasonable request as your supervisor or they’re asking you for a favour. If the former, it’s literally your job to do wh

It depends whether someone is making a reasonable request as your supervisor or they’re asking you for a favour. If the former, it’s literally your job to do what they ask and if you can’t, you need to give them a reason why not. If the latter, ‘no’ is fine… but I wouldn’t use this too often with anyone I might ever need a favour from in return.