Requirements order: from chaos to FIFO

Many companies, working both with classical development methodologies and using Agile approaches, risks to get in a trap of the order during working with requirements. This is dangerous especially there, where is much more difficult - even not impossible - to plan the process of creating the specification or the final product due to increased variability of requirements focus  that the customer can change daily.

I want to tell my experience of refusal from a flow generated by the customer on the basis of some of its priorities and the transition to the FIFO queue (First in - First Out).