Imagine I'm a rogue and I see an opponent 50' away. In my turn I want to use my movement and my Dash bonus action (Cunning Action) to approach it and use my Action to attack.
Then, after moving just 10' (or more, I guess it may change the answer), another opponent had readied its action so as a reaction it attacks me, and hits me so hard I don't want to go hit that opponent anymore.
- Can I just stop my current movement and move elsewhere/back?
- Do I have to finish my movement and then use the Dash to move away? If that's the case, I assume it depends on how much I've moved to know what can I do.
- Does changing this imply some sort of penalty?
This is just an example, but the question isn't referred exclusively to movement. It could be attacking and then using the bonus action to Dash instead of hitting again. As noted by the chosen answer, it was related to "declaring and acting" and "changing what I declared"