Why is life so important? When asking around, I've never heard anyone agree that a young, healthy person should end their life by suicide. But I also don't know what reason there is for that consensus. 

Did Buddha teach anything regarding what makes life worth living?
The first book I read about Buddhism described the Sermon at Benares, i.e. the Dhammacakkappavattana, as explaining that the cause of suffering (the second noble truth) is,

... the craving to have what you don't have; the craving to keep what you can't keep; the craving to live; even the craving to die.

And here is the same quote from Access to Insight,

&quot;And this, monks, is the noble truth of the origination of stress: the craving that makes for further becoming — accompanied by passion &amp; delight, relishing now here &amp; now there — i.e., craving for sensual pleasure, craving for becoming, craving for non-becoming.
&quot;And this, monks, is the noble truth of the cessation of stress: the remainderless fading &amp; cessation, renunciation, relinquishment, release, &amp; letting go of that very craving.

So I think that suicide must be missing the most important, fundamental truth of Buddhism.
Suicidal ideation is a risk factor: Suminda said, &quot;You shouldn't even think about things like suicide&quot;.

Similarly, the &quot;middle way&quot; doctrine says not to afflict or self-mortify the body.
And, the doctrine of rebirth suggests that, although there are problems in life, these problems can't be escaped simply by dying. It was by 'unbinding' (not suicide) that in the Ariyapariyesana Sutta the Buddha said,

I reached the aging-less, illness-less, deathless, sorrow-less, unexcelled rest from the yoke: Unbinding. Knowledge &amp; vision arose in me: 'Unprovoked is my release. This is the last birth. There is now no further becoming.'

According to the Vinaya even 'describing the advantages of dying' is wrong.

This, the third type of act covered by this
rule, can include [...] telling a
person of the miseries of life or the bliss of dying and going to heaven in such a
way that he/she might feel inspired to commit suicide or simply pine away to
death. [...] Thus, the Commentary notes, a bhikkhu talking to a dying patient should be
very circumspect in how he chooses his words, focusing not on how to speed up
the dying process but on how to inspire the patient with the following thoughts:
“The attainment of the paths and fruitions is not out of the ordinary for a
virtuous person. So, having formed no attachment for such things as your
dwelling, and establishing mindfulness in the Buddha, Dhamma, Saºgha, or the
body, you should be heedful in your attention.” The Vinita-vatthu to Pr 4
contains a number of stories in which bhikkhus comfort a dying bhikkhu by
asking him to reflect on what he has attained through the practice, which was
apparently a common way of encouraging a dying bhikkhu to focus his
thoughts on the best object possible. The suttas also contain advice on how to
encourage patients facing death. See, for example, MN 143, SN 36.7, and AN 6.16.
In all of these cases, the advice is aimed not at precipitating death but at inspiring
calm and insight.


As for &quot;what makes life worth living&quot;: Buddhism can even seem quite 'negative' (&quot;life is suffering&quot;) ... and so I asked this question, How to explain what Buddhism is? ... and people's answers to that explain it in more 'positive' or constructive terms: morality; concentration; and wisdom.
My dad told me, when I was young, that suicide is painful for the friends and family who are left behind (i.e. it causes suffering for others): I thought, even that is enough reason to avoid suicide.
And, for example, I lived with a friend: who became relatively enlightened, especially during the last year of her life. So it was more perfect, for her and for others, that she lived as long as she did, instead of dying earlier.
Perhaps what makes life worth living is that it's an opportunity to &quot;live the holy life&quot;.
Many Buddhist descriptions try to describe the experiences of one person (e.g. in meditation), or even of 'no self'.
But part of the &quot;holy life&quot; is in the relationships between people, for example,

As he was sitting there, Ven. Ananda said to the Blessed One, &quot;This is half of the holy life, lord: admirable friendship, admirable companionship, admirable camaraderie.&quot;[1]
&quot;Don't say that, Ananda. Don't say that. Admirable friendship, admirable companionship, admirable camaraderie is actually the whole of the holy life.

Perhaps you don't feel you have that (or are that) at the moment but there is every chance you might in future.


Unfortunately there are things which can make life seem unimportant: bad companions, &quot;heedlessness&quot;, &quot;restlessness&quot;, etc.
Instead, try to remember what Right intention is:

And what is right resolve? Being resolved on renunciation, on freedom from ill will, on harmlessness: This is called right resolve.

Also, problems are fixable: problems, too, are 'conditioned' and therefore changeable.