I’m currently working on the third book in a space opera trilogy. One thing I learned early on is that characters must be believable and that readers must have a stake in them if you are going to get very far.
…Especially if you plan to write a multi-part book series with them….
One trick to giving them depth is to wound them or give them some flaw that allows you to dig deep into their psyche.
Here’s the best reasons for this:
- Recurring Problems – If your character is wounded because of something they did or if they are somehow different because of this wounding, you will create instant recurring conflict for them down the road. They will never get over it, or getting over it will take major work for them.
- Sympathy – A wounded character is often someone that a reader has zero difficulty becoming attached. We all love characters with deep flaws. It makes them more relatable.
- Greatness – Flawed characters, when they finally manage to overcome their flaw even slightly become heroic. Its why we all make New Year’s resolutions. We want to be better. Seeing characters achieve greatness however small gives us hope.
Writing Is Hard Work 
Solid and concise advice, Roger.
Funny that you/we realize this in writing and in the reading experience … and then spend so much of our lives trying to hide our own flaws, failures and generally “ugly.”