Most people never consider how the horse responds to just the sight of tack or notice if there are Quality Conversations while doing so.
Each part of the interaction influences the mental reasonableness and physical softness that follows.
While the norm (often out of convenience) is to tie the horse while tacking, the degree of bother or concern a horse may have while doing so frequently is suppressed.
I suggest practicing tacking the horse without tying him. The goal is not about getting tack on.
It is an Opportunity to notice how your horse feels about standing while you are moving around him.
It also allows you to observe for things such as:
Does he mentally check out as you go to groom?
Does he pin his ears, shake his head, swish is tail, or display any other defensive behavior as you groom?
Does he step away or backwards when you swing the pad or saddle on?
Does he constantly avoid the tacking by diving down for grass?
When you tighten the cinch or girth does he swing his head at you, try to walk off, back away, etc.?
Does he act differently if you tack from one side versus another?
If you change the location of where your horse is as you tack does he suddenly act differently?
None of this is about the unwanted behaviors. Instead the undesired responses could be an indicator as to potential pain issues, holes in the foundation of the equine partnership, reflection of concern towards the upcoming ride, etc.
If the ride is prefaced with an experience (in this case tacking up) causing the horse to be in a state of anticipation, defensiveness, avoidance, flee, etc. how might that influence everything asked of him during the ride?
There is never a convenient time to address the horse's concerns, but the longer you avoid helping him, he is being taught he is own his own. This will cause him to start taking over and dictating how the interaction will go based on the lack of support, or even criticism from the human.
The horse only has so many subtle, reasonable behaviors to display his fear, concern, or anticipation. If you're not addressing it now, then when?