I dug through my logs to compare the skill improvement rates of Infiltrate and
Pick lock. The numbers that came up suggest Infiltrate's skill improvement rate
is broken as it never gains any % through failures, unlike Pick Lock and many other
skills.

The improvement rate on success is also vastly lower, which might be a
result of needing to Infiltrate lower level locks to have a chance at any skill
improvement. While likely not a bug, it is possibly an unintended side effect.


SKILL LEARN FROM SUCCESS

You focus intently upon XXX, and the lock just happens to pop open.
Infiltrate success, 543 instances.
Skill increases from success: 12

You hear a near inaudible *click* as you skillfully pick a XXX.
Pick Lock success, 145 instances before perfection.
Skill increases from success: 12

Takeaway:
The learning rate for infiltrate seems to be considerably lower than Pick Lock.
See "Locks beyond your comprehension" for theories why.

==============================================================================

SKILL LEARN FROM FAILURE

You failed to infiltrate XXX.
Infiltrate failure, 176 instances.
Skill increases from failure: 0 (Expected value)
Skill increases from "learn from your mistakes": 0 (Unexpected value)

You failed to pick XXX
Lockpick failure, 257 instances.
Skill increases from failure: 0 (Expected value)
Skill increases from "learn from your mistakes": 10 (Expected value)

Takeaway:
The learning rate for Infiltrate appears to be broken here, as you never gain
skill increases on a failed infiltrate, either by "learning from your mistakes"
or by standard 1% gains on use.


===============================================================================

SKILL LEARN FROM "LOCKS BEYOND YOUR COMPREHENSION"

You focus intently upon XXX, but nothing seems to happen.
Infiltrating impossible lock, 56 instances.
Skill increases from attempt at impossible lock: 0
Skill increases from failures: 0

This lock is beyond your comprehension.
Picking impossible lock, 52 instances.
Skill increases from attempt at impossible lock: 0
Skill increases from failures: 0

Takeaway:
Zero gains as expected, but...

Interestingly, the threshold for "lock beyond your comprehension" seemed much lower
on infiltrate than lockpicking. This means you must attempt infiltration on lower
level locks to have any chance at improvement, which may diminish your likelyhood
of increasing the skill by use (assuming harder locks give you a better chance of
improving the skill, the same way harder mobs do for other skills).

You focus intently upon a hidden door, but nothing seems to happen.
You hear a near inaudible *click* as you pick a hidden door.
Your ability in the skill infiltrate is at 82%(82%).
Your ability in the skill pick lock is at 83%(83%).
Your ability in the skill advanced picklock is at 78%(78%).

===============================================================================

Final conclusion:

Learning rates from success:
Might be lower due to needing to practice on low level locks since even slightly
challenging locks are beyond comprehension.

Learning rates from failure:
Seems broken, never learn from mistakes

Learning rates from impossible locks:
As expected

Went and tested, I learned it fine.

You can't learn infiltrate off of locks you could never infiltrate.

You don't learn better because a lock is harder.