Having a positive attitude does not mean that you are dismissive of problems and concerns while others who are pessimistic are more mature and realistic in the face of undesirable circumstances. A positive attitude is driven by a belief that successful outcomes and solutions to problems are often influenced by optimism. A person with a positive attitude is a learned skill, valued by employers, and often mentioned in performance reviews. If your attitude is easily affected by circumstances, try practicing "conscious positivity."  When you don't quite feel like being positive, be excited for others' achievements. Have fun playing cards when you are losing. Be friendly to others you don't know. Motivate others by saying something positive. Avoid letting others' negativity bring you down. And, ditch the "yeah, but..." With practice, you'll get the hang of it fast.