Things you learned about a Job/role by not playing it

[Pells]

LOL makes me wonder if they played EverQuest. There you had to sit to initiate the meditation state so you would regen your mana pool.

With the spellbook open, so you couldn't see what was going on either.

[tymora]

Learning to change targets if tank comes close to losing it.

[caelumsixsmith]

Healers and tanks get commendations (healers from everyone, tanks from healers, usually) while DPSs don't and if they do, that's very rare. Oh, and tank is difficult. I'll probably give up on it if I unlock PLD and still can't manage to keep aggro on me.

[Rennies]

Gladiator has an extremely hard time taking aggro and doing damage.

I like Dark Knight infinitely more at lower levels.

[The_NPC]

thou I have never got the following classes to lv60, my RL/FC friend has & main's them: my respect for a WAR or SCH/SMN that can do so much extra effort & see something for it (& my respect for comunication as we use PSN chat when in-dungeon together, I use WHM or PLD respectivly in most cases makes both our jobs easyer on high dmg fights like uber-pulls)

I did learn about certian ways to "cheese" mechanics as PLD by seeing another PLD do it back in 2.0, as for positonals & proper Def CD managment I just learned those by lv'n PLD (as it was my 1st class, MNK/BRD/BLM were 2nd didn't pick up WHM till 2.4... didn't start DPS'n in-dungeon with it till 2.55)

[Averax]

When playing a DPS for the first time in forever during what should have been a simple void ark run has taught me that pug healers are not to be trusted.

[Knahli]

At least in PvP, I learned what Attunement was in the early days of 72-man Secure when I finally decided there must be some short timer happening that is making said healers seemingly impervious to my attacks. Needless to say, I noticed it and felt a lot better about finally understanding why my attacks weren't going through.

I also partially learned that Provoke was super good for Tanking in Garuda EX but I assumed it just gave you a ton of aggro so the actual workings of it weren't figured out until much later after lots of trial and error.

[Reinha]

I learned how nice Foe Requiem is by playing casters and how unnecessary Mage's Ballad is by playing healers.

Whilst leveling DRK I learned to check the tanks buffs before Holy spamming mobs.

I also learned the importance of not rotating or kiting mobs needlessly when tanking after leveling a few melee classes.

[Shurrikhan]

Not putting regen on the tank pre-pull on healer. It's not impossible to deal with it (even without clicking it off),
but I sure as heck had a really hard time catching all monsters that made a beeline for the healer as soon as they saw me when I played tank.

Sometimes the opposite for me. If the tank is going to pre-pull, I can either sprint-drag the mobs to where the tank wants them to go, in which case Regen is fine and ideal for others being able to pop DoTs on the few he does grab with actual enmity, even if it means the tank has to move off the quickest way to the gather point, or I can just run ahead and ready a Holy, Gravity, or Bio II pre-cast. I didn't realize how clear the cut is though until doing speedruns from both perspectives. Either allow the face-tanking, or tank yourself (really just gather mobs for the tank's ease of tanking).

The healer's perspective also taught me when my stance-dancing really isn't costing nearly as much as the healer (who spends half the time idle and refuses to HoT) would have me believe.... Sometimes the shock therapy of forcing him or her to use more than just Cure/Physic/Benefic has lead to smoother experiences over the rest of the run, even if my life was never at risk. Scholar further taught me that I rarely actually need a tank in 4-man content, unless the lead enmity dps insists on taking TBs in BFB, simultaneous with a critical strike auto-attack. So if they're holding up a pull by more than their personal dps and positioning could aid rDPS, rudely and/or overly frequently, I will pull, usually to the DPSs' satisfaction.

[JunseiKei]

First two things I learned from playing healer:

1) Using Fluid Aura or any other knock-back skill on mobs is a melee's worst nightmare when it doesn't kill the monster. Especially when the user of knock-back isn't being hit.
2) Learning when a tank buster is coming and when to Stoneskin for a little extra mitigation.

Countdown timers are a blessing for openers.

When tanking, it's nice to always be on the move and not waste time in between pulls (great for summoner, monk and ninja).