You may underrate the power of hope, but that will definitely be at your own peril. The fact will always remain that, nobody knows what tomorrow holds, but have to make plans today for it. By all perspectives, when you're making plans for a tomorrow that you're not certain will come - this is having hope.
Most poor people never achieve much in life, not because they're not hard working, but because they don't have enough hope. They squander their money today, saying 'what if I die today?'. When you see a great man, you see a man that is hopeful about almost everything. It's very easy to start imagining the worst outcome in the future.
But a successful man, makes effort to think positively about the future, because he is filled with hope, that what he desires and plans for will come to reality. If a farmer wants to sow a seed, and starts thinking what if rain doesn't fall?, what if diseases and pest destroy the plant before harvest?, what if flood came?. Such a person may not even sow that seed.
The endless possibilities of things going wrong will forever be there, you just need to be very hopeful as a person to do what you should do. Lack of hope is what makes the traders in the markets to panic quickly and sell off their assets, and in most cases after they sell at a loss, the price makes a U-turn and starts going back up.
Of course, you should be very careful what you're hopeful for. That's why there's a saying - be careful what you wish for, it may just happen. If whatever you're hoping for is not realistic, no matter your power of hope, it will not come true. So you have to carefully analyze where you place your hope, so that you're not just a wishful thinker.