Field mapping in Merge Tool

[AmeliaNewsam]

I'm merging a bunch of feature classes (400) and trying to understand the Field Map settings.  I need to map multiple input fields onto one output field, but I can't figure out how to do that (it looks like I have to do it for each feature class individually, which can't be right).  I've read the ESRI help page, but it just didn't go into enough detail for me.  If some kind soul could step me through the process, I would appreciate it.  Or if there's an ESRI tutorial that would help, I'd be grateful for the title.  

[AmeliaNewsam]

OK, I do actually understand what you're saying now (just took a few minutes to sink in), but I still am not sure how to select the source field from all the files at once.  I think I tried just selecting it from one file, and it ended up mapping only that one file.  I'm sure it's just a simple thing I'm not understanding, but it's hard to communicate what that thing is.

[DanPatterson_Retired]

that is how you map... one file at a time, there is no mention of matching one file to many in the help

Attribute field mapping—ArcGIS Pro | ArcGIS Desktop 

[AmeliaNewsam]

But it should be a simple enough thing to do, right?  I mean to put that capability into the software.  If it can move data from one field to another for one file, it should be a simple thing to allow it to move multiple fields.  But maybe it's not something people need to do often enough to make it worthwhile for ESRI to do.  

[DanPatterson_Retired]

Everybody's 'use-case' is unique.  What is one person's main workflow isn't another's.  I rarely make maps, but I use gis analytical tools extensively.  And I create my tables outside of Arc* and bring them in only as needed.    Coding can be a solution but it is not 'the' solution.  Good luck

[AmeliaNewsam]

Thanks Dan!