I’ve always felt responsible for making such a big deal about the differences between estimated and actual plans. I implied in the first edition of the execution plans book (get the new, vastly improved, 3rd edition in digital form for free here, or you can pay for the print version) that these things were so radically different that the estimated plan was useless. This is false. All plans are estimated plans. However, actual plans have some added runtime metrics.
It’s not that we’re going to get a completely different execution plan when we look at an actual plan, it’s just going to have those very valuable runtime metrics. The problem with getting those metrics is you have to execute the query. However, this is no longer true in SQL Server 2019 (CTP 2.4 and greater) thanks to sys.dm_exec_query_plan_stats.