Objection 1. It would seem that experience is not a cause of hope. Because experience belongs to the cognitive power; wherefore the Philosopher says (Ethic. ii, 1) that "intellectual virtue needs experience and time." But hope is not in the cognitive power, but in the appetite, as stated above (Article 2). Therefore experience is not a cause of hope.
Objection 2. Further, the Philosopher says (Rhet. ii, 13) that "the old are slow to hope, on account of their experience"; whence it seems to follow that experience causes want of hope. But the same cause is not productive of opposites. Therefore experience is not a cause of hope.
Objection 3. Further, the Philosopher says (De Coel. ii, 5) that "to have something to say about everything, without leaving anything out, is sometimes a proof of folly." But to attempt everything seems to point to great hopes; while folly arises from inexperience. Therefore inexperience, rather than experience, seems to be a cause of hope.
On the contrary, The Philosopher says (Ethic. iii, 8) "some are hopeful, through having been victorious often and over many opponents": which seems to pertain to experience. Therefore experience is a cause of hope.
I answer that, As stated above (Article 1), the object of hope is a future good, difficult but possible to obtain. Consequently a thing may be a cause of hope, either because it makes something possible to a man: or because it makes him think something possible. In the first way hope is caused by everything that increases a man's power; e.g. riches, strength, and, among others, experience: since by experience man acquires the faculty of doing something easily, and the result of this is hope. Wherefore Vegetius says (De Re Milit. i): "No one fears to do that which he is sure of having learned well."
In the second way, hope is caused by everything that makes man think that he can obtain something: and thus both teaching and persuasion may be a cause of hope. And then again experience is a cause of hope, in so far as it makes him reckon something possible, which before his experience he looked upon as impossible. However, in this way, experience can cause a lack of hope: because just as it makes a man think possible what he had previously thought impossible; so, conversely, experience makes a man consider as impossible that which hitherto he had thought possible. Accordingly experience causes hope in two ways, despair in one way: and for this reason we may say rather that it causes hope.
Reply to Objection 1. Experience in matters pertaining to action not only produces knowledge; it also causes a certain habit, by reason of custom, which renders the action easier. Moreover, the intellectual virtue itself adds to the power of acting with ease: because it shows something to be possible; and thus is a cause of hope.
Reply to Objection 2. The old are wanting in hope because of their experience, in so far as experience makes them think something impossible. Hence he adds (Rhet. ii, 13) that "many evils have befallen them."
Reply to Objection 3. Folly and inexperience can be a cause of hope accidentally as it were, by removing the knowledge which would help one to judge truly a thing to be impossible. Wherefore inexperience is a cause of hope, for the same reason as experience causes lack of hope.
Source: Summa Theologica (New Advent)