what, after all the negative reports we have had, keeps that optimism alive.

'Negative reports'?
Unless you've something specific, most of what we hear from remainers are reports of negative forecasts. Just as we can't give the positives until we are in a post Brexit situation, you will not know the accuracy of those forecasts until the same time.
Our voting (or mine at least) was not purely based on optimism. There was also pessimism about the future of the EU and our relationship with it. That pessimism was based on the results of decades of membership of the EU.

A woman doesn't have to know what her future position will be in order to get out of a bad marriage. It may be enough just to decide she wants to get out. Although, as I understand it, many women can't make the decision to get out, and remain in abusive marriages although they know nothing will get better, and it may well get worse.

The latest news from Theresa May does not fill me with confidence, but I still want to see us break our (current) ties with the EU.

DMcG: However, if you want anyone else to share that optimism, you need to explain the foundations of it to them. Is that difficult to understand?

It is not my job to persuade you of the benefits and convert you to my optimism. You can continue being pessimistic. Enough people already feel that we would be better getting out of the EU (for one reason or another, and yes, there may be some xenophobes among that number) for the Brexit referendum to have been won.