Is there a reason some quests will not complete even when you do what it says?

I may not understand the format on which to complete things properly but could someone explain why some things just won't complete? Just a general question I am trying to understand things. Like I also can't figure out why some drops are not equipable even when it's the same type... I think

If by Quests, you mean Client Orders, then it is often because some Client Orders have specific requirements, such as enemy level or Quest difficulty, and occasionally they are either missing from the CO description or are labeled incorrectly.

As for equipping, you have two things to consider: Class and Base Stats.

  • For example, if you are a Hunter, you will not normally be able to equip weapons that are not Swords, Partisans, Wired Lances, and Gunblades; occasionally you may come across some off-class weapons that can be equipped, but those are the exception rather than the rule (you can check the second tab of the item description to see which classes can equip a weapon).
  • On the first tab of an item, you will see a line that says "Req [some stat] / x (Current value: y)"; the "y" is the base amount you have the stat you need to equip it, and this number is separate from total amount of the stat you have as seen in your Character Stats screen. Base Stats only include character level, Mag level, Stat Up Skills from your active Skill Trees, and lv75 Title Bonuses, while Total Stats include Base Stats, Weapon stats, Unit stats, Ring stats, Augments, and any boosts (like from Drinks or Food items).

Also want to add that if an NPC sends you out to kill x monster, sometimes it’s a specific elimination quest from the counter, not just killing the monster in expeditions.

For example, Afin’s newbie quest tells you to complete Suppress Phongruff, this is actual quest name, you can’t just slay random Phongruffs. A lot of newcomers had trouble with this and I’m sure it still happens with other quests. Double-check the quest name and look under sub quests just to be sure.

some client orders will have you needing to be a certain class an/or have a certain npc character with you to complete it.

There also that some require you to reach a certain rank at the end of the mission, that being A or S rank.

There are even ones that require you to kill certain number of enemies while a certain class an using a certain weapon

Need to read all the client orders details to know what you need to do.