Requirement

General
Main items as well as off-hand items pose an attribute requirement in order to use them to their full benefit. It is a common misunderstanding that items for which a player does not meet the requirement do not give any benefit at all - the gain is mitigated somewhat, but not obliterated completely:
 * For melee weapons, bows and spears (see the different skill types), the min. and max. damage is reduced by 1 for every point the requirement is not met. Example: A Warrior wielding a max dmg Axe (6-28) with req. 9 in Axe Mastery will only do 4-26 damage when having his Axe Mastery set to 7.
 * Off-hand focus items that provide a energy bonus have their gain mitigated based on the value of their requirement. The following table consolidates the observations from several testers, which were also confirmed by others:


 * It should be noted that Energy gain that is not tied to a requirement is not mitigated. This kind of gain can occur from inherent item properties, for example staves, or from inscriptions.
 * For example, the Grim Cesta given by Symon the Scribe. Assuming that your health is below 40% and you are hexed and enchanted, but that you have 0 ranks in Blood.  You would have a mitigated gain (E+3) from the Cesta's inherent energy, but you would also gain 11 Energy (3+3+5) for meeting the conditions.
 * Grim Cesta (given by Symon the Scribe for completing Cities of Ascalon)
 * Energy +6 (req. 5 Blood Magic)
 * Health -50
 * Energy +3 (while enchanted)
 * Energy +3 (while hexed)
 * Energy +5 (while Health is below 40%)

Preliminary Conclusion

 * Speaking in general terms, there seems to be a "mitigated gain" cap (that is, the absolute maximum energy gain when not meeting the requirement) of a total of 6 energy.
 * 1 Green items, items obtained from a Collector, and quest rewards seem to have their own mitigation, differing from other drops including golds. The most common, req. 9 items, seem to be mitigated to 25%, providing only E+3 if the req is not met.
 * Be aware that Weakness causes all attributes to drop by -1, so meeting the req. demand by even +1 should be the wisest choice, especially when equipped with one of the wide-spread req. 9 items.

Note

 * Keep in mind that if someone is selling an item or offhand that has a very high requirement, the price should be lowered down.
 * Even if some items have a very high requirement, you may still be able to use them. You can always buy runes to upgrade your current skills.
 * If you are a very high-level player who is fighting a lower level enemy or monster and do not have a high enough skill requirement for an item, you may still be inflicting high damage against that opponent, but keep in mind that this is only caused by the level difference between the two of you.