break it down what did he mean by "think"? was it some word based sentence? possibly was it a concepulization? possibly was it an emotion? possibly was it a feeling? possibly was it a perception? possibly was it being conscious of something? possibly then the statement collapses and becomes redundant A=A
but if one views descartes dictum as a description of how most people tend to create themselves, then it is spot on. i'm a loser, i'm a winner, i'm god, i'm somebody. really?