Maybe it feels unsafe because it is - it's a risk. When you're assertive things can change, not necessarily the exact way you wanted. Then you have to adapt to something different, something I'm not terribly fond of. I'm pretty assertive though. I feel compelled to act in most cases. I'm that unreasonable person who wants to change the world (in small ways, but I wish they were big ones) rather than adapting all the time. (Maybe you don't have my issues with being rigid and inflexible and even a little bossy.)

A loss at what to do? Start with the smallest and simplest thing. When you say no, DON'T explain. All you have to do is withold your action and feel. And figure out what you're going to do with your mouth, hands, eyes, rather than babble explanations. (I do the unnecessary TMI thing, too.)