Being nice and being a pushover are different. Kind people still say no.

Niceness is often just conflict avoidance wearing good manners. Kindness is harder, because it involves actually caring what happens to someone, which sometimes means refusing them. The person who says yes to everything is not being generous, they are managing their own discomfort, and the people around them learn that their yes means very little.

Practise the warm no on something small this week: a lift you cannot give, a shift you cannot cover, a favour that would wreck your evening. No elaborate reason required. Keep the tone kind and the answer unchanged.