Not true at all. People have been offered promotions which involved a significant change in direction for their career and have refused those and have had their career continue just fine. In real life. Say an intelligence officer, currently serving as the S-2 in an infantry BN, is offered the chance to become a company commander in that infantry BN (and yes, that does happen sometimes) by the BN Commander. Perhaps that officer would prefer to be in the division G-2's office and has no desire to be a tactical commander. Sometimes it's just a matter of choosing a career path. And I can tell you, in those cases, it's most certainly NOT "career-ending."