Whenever I have heard any manager address a project team and tell them to “Just do it”, I know that it’s unlikely to be a successful endeavour, and it almost certainly won’t be Agile.

When said by the manager, “Just do it” typically means:
- the team is told the scope of what they must deliver and by when
- the manager is not working with, or listening to, the team
- the team is given a detailed and overly-optimistic plan
- the customer is not engaged with the team
- the team members work in isolation to only deliver their tasks
- and the manager measures daily progress by the effort spent

This is obviously going to result in some bad team behaviours and poor results where:
- the team abandons a disciplined approach and starts hacking
- the team no longer takes ownership for the solution
- the team’s morale is lost and productivity drops
- reduced collaboration results in poor communication
- individuals blindly follow a given plan
- and the manager is surprised at the end of the planning period when the “team” fails

So please, don’t encourage your software project teams, or let yourself be told, to “Just do it”.
Get smart and “get” Agile.