Sometimes, it seems that your own disinclination isn't a valid excuse for refusing. Especially to refuse a good or familiar person.
Even though, I have to tell you that your own unwillingness to do something is a good reason to say "no" to someone.
Ultimately, we are forced to do something without pleasure or desire, and most importantly, for another person. And what about you? What about your feelings and desires?
You will not feel anything but anger and irritation towards those whom you couldn't refuse if you do this often, neglecting the only closest person, yourself. And you will also be angry at yourself for doing so.
However, it is also true that it can be challenging to simply state, "No, you know." It is, in fact, not an easy task. Especially when someone asks you something politely and insistently.
I will give you one life hack: you can always take a legal pause before answering someone. It is much easier than refusing immediately.
For example, someone asks you about something, and you respond, "Yes, I understand you. But I will be able to answer you in an hour, a day, tomorrow evening. Is that okay? I need to think. I need to clarify my plans. Currently, I really can't give you an answer. Too quickly." After the time you took to think, it is much easier to respond with a refusal and the person will find it much easier to accept such a refusal: "Listen, I have thought it over, I won't be able to."
Parents, practice together with your children to protect personal boundaries and speak "NO" correctly, use our exercise, and you will see - it works.