Riddle

[deguspice]

Here's a riddle that came to me in a dream about a car club last night:

The more you use this, the more you have. What is it?

The answers will be screened until someone finds the answer I had in mind.
(I'll be interested to see if someone comes up with a different answer that works for the question)

Edit:

I've unscreened the answers. You had lots of good answers, including a couple I weren't expecting, I've added my answer to the comments below (feel free to add your answer before you view the comments).

Comments

[chanaleh.livejournal.com]

Muscle tissue? :-)

[goddessfarmer.livejournal.com]

Love is the first thing that comes to my mind.

[whuffle.livejournal.com]

Cope?

I've noticed that people's threshold for coping gets higher the more times they push themselves to the limits thereof.

[drwex]

Experience

[cloakmaker.livejournal.com]

Experience

[donnad.livejournal.com]

Intelligence, smarts, education...

[weegoddess.livejournal.com]

Hmmm.

Kindness.

Love.

Generosity.

Aching joints.

Stained cookware.

Flower seeds.

A keen wit.

(how am I doing?)

[batwrangler.livejournal.com]

Skill.

[deguspice.livejournal.com]

The answer I had in mind was "compassion".