Our company has a new manager, who is eager to prove himself. During our regular meetings everyone is encouraged to take on more tasks and to grow. That's not unusual in any way but I don't have any more capacity. And, to put it mildly, the problem is that the manager is oversimplifying the tasks to make them sound doable like:
Manager: Why don't you get a software certificate in X?
Me: Project A is taking up most of my time, and I'm helping out with project B as well.
Manager: That's not a problem - you just spend an hour a day studying and in several months you are an expert and you'll get that certificate easily. It's very easy, isn't it?
Me: I cannot leave projects A and B.
Manager: Don't tell me you can't find an hour a day?
Please note he's not asking me to change priorities but to take on extra tasks, which I know will take time and effort.
In what situation is it appropriate to answer with a straight "no"? Any examples where you go straight to the answer without wasting time?
Edit: I'm talking about extra tasks, "walking the extra mile" thing.