A simple and seemingly dull idea can disrupt the industry. A groundbreaking idea may never see daylight.
So stop evaluating the idea and hanging to a single idea. The goal is to generate as many cohesive ideas in the range of being practical to impossible. This lets you see everything in the spectrum.
As per James Altucher building the habit of writing down 10 ideas (or more categories to spice it up) every day builds your creativity muscle and gets the creative juice flowing.
If you can't generate 10 ideas, generate 20 - James Altucher
James Altucher also keeps an action tab for each idea - the first step to get the idea further. It is hard to generate unlimited ideas that you perceive to be good or great. However, it is not that hard to generate ideas that fall in the range of good, great, mediocre, dull, bad, crazy, impractical, and unrealistic.
Maya Angelou puts it,
You can't use up creativity. The more you use it, the more you have.
It is equally hard to randomly think and generate 20 ideas. But if you can categorize or put a structure to your idea sources, you may be able to unearth a couple from each category
From your yesterday's experiences at work, home, outdoor or elsewhere
From reading a book
From reading news or articles
From free/random thinking
From other people
From the problems, pains, and promises you and your world faces every day
Once you have a corpus, you have to see if your idea really solves anything for your customer. It needs to do that job. There is no way around it. Pick a few in that range and proceed. Use the "Jobs to be done" framework to see if you are solving your customer's needs. Did you generate the idea from a customer's point of view? Then ask more customers.
Then among the shortlist, you need to pick a few viable ones. Viability means that you have to don the shoes of different people and tools that your idea will go through before becoming reality. Is it viable to you? Is it viable for your customer? Is it viable with the tools you have?