These issues are common in any industry. There will always be people that are unavailable due to vacation or sick leave. This can impact the life-cycle of the project and possibly delay some parts of the process. The key to mitigate delays due to these issues is by establishing proper communication. Once proper communication is established, there is follow-up on the work that needs to be done. For example, if I am taking a vacation for a week, I would let the project manager know and delegate my work to someone that is capable of fulfilling the tasks assigned to me. At a higher level, when in the planning stage certain steps should be given a decent amount of time to account for this. When a project is in the summer months, when employees typically take vacations, the time allotted for tasks is generally increased due to these reasons. In the end, we’re all human, we have other obligations, but to ensure nothing is interrupted, proper communication must be established.