Planning phase should cover as many pitfalls as possible for the project to complete but however hard you try its not possible to cover all of them since once you actually start doing the work you feel like the deadline is too close or it is not achievable so you will need to go and discuss to project manager and make sure you re-evaluate your planning phase so what this re-evaluation actually shows that you are making progress in your work. As told above to much planning and re-evaluating leads to poor progress of project so it always important to invest some time early on to think and plan the work and than decide a deadline which is not achievable and try and avoid making to many changes in planning phase.