As you noted your question using ASP.NET, here is the required document:
ASP.NET Page Life Cycle Overview
When an ASP.NET page starts up, the page goes through a life cycle (steps) in which it performs a series of processing steps. These include initializing, managing instances, restoring and maintaining state, event handler code, and rendering. This is important for you to understand the life cycle of the page so that you can write code at the appropriate stage in the life cycle for the effect that you intend.
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