When you use a blender, it’s important to act decisively. This is perfectly compatible with acting gently, of course, if this is what’s required.
Gentle decisiveness will get the job done (while indecisive gentleness is just the same as dithering).
That’s why we usually hold our blender as you see right here:
Now whether you grip with three fingers (as shown) or four is not important (it will in part depend on the length of your fingers).
What is important is that those fingers (three or four) push the shaft of the brush against the base of your thumb. And that your thumb grips back.
With a really good grip like this, your also adopt a firmer frame of mind. And this will help you move the wet paint decisively and confidently to where it should be.