The Spleen governs the thought. Mental processes such as thinking, concentrating, studying, and focusing are governed by the Spleen. When the Spleen functions in a warm and dry internal environment the thoughts are clear, practical, and beneficial. Deficiency of Spleen Qi – the most common Spleen pathology - leads to overthinking – thinking about the same over and over again with difficulty to resolve the thought or let go of it. Dampness in the Spleen – the complication of unresolved Spleen Qi deficiency - furthermore leads to “damp”, “sticky” thoughts that glue to the mind and oppress the mood.
Some more info here https://holosapiens.com/mentality/pensiveness-mentality