Although Shaul HaMelech was a Tzaddik Gamur, we still have to learn not to be like him, since for good reason he lost the Malchus; we have to be like Dovid who remains our true Melech. Shaul was suspicious, and he believed that everyone was against him. It wasn’t true at all! Dovid actually loved and respected him, despite the horrific Redifos (persecution) and Tza'ar (distress) that Dovid suffered from Shaul. And nobody was plotting to kill him.
Dovid was the extreme opposite. He loved and trusted even his worst enemies, like Shim'i ben Gera, Shaul, Avner, and Avshalom. And he was frequently wrong. For example, he allowed his son Amnon to go to Avshalom’s party, and he didn’t suspect that Avshalom would kill him. It is indeed a big Kashya, since Amnon had tortured Avshalom’s sister Tamar, and Avshalom wasn’t on speaking terms with Amnon.
Both the “always-suspicious” types and those who are “trusting” are often wrong, and we all need a healthy balance of: כַ בְ דֵ הוּ וְ חַ שְ דֵ הוּ (respect yet suspect). Nevertheless, we all need to be closer to the Derech of Dovid and to see only good in others. The Gemara says that a person has to be Dan people L'kaf Zechus even to the extreme. Especially if your nature is to be suspicious, you need to work on your Middos and go extreme in the opposite direction.
