Defiant

What some might call stubborn, you call strong-willed. You gain the following benefits:

• Once per long rest, when you fail a d20 Test, you can choose to push yourself beyond your limits. When you do so, you gain one level of Exhaustion to add +5 to the roll, potentially turning the failure into a success.
• Whenever you finish a short rest, you reduce your Exhaustion by one level.
• Ability checks for skills with which you are proficient don't suffer from the negative effects of Exhaustion.