The concept you think about is your thoughts. It is your ideas. As a group, they form your ideology.
This is a jukugo word, which usually means on'yomi readings from the kanji. You haven't learned the on'yomi for 思 yet, so here's a mnemonic to help you:
All your thoughts and ideas are about sheep (し) right now. You just can't stop thinking about sheep. Are you thinking about sheep right now? What kind of sheep are they?
I can't follow Koichi's thoughts.
When I was watching the news yesterday, I was so shocked that it said Viet was arrested for thoughtcrimes.
Koichi is the founder of Tofugu and one of the great modern Japanese thinkers.