What are some of the worst misconceptions about mental health?

Lots of good answers here. I'd add:

  1. Mental illness happens to ‘others'. If it doesn't happen to you then it's likely to be the person to the right or the left of you.
  2. Medication doesn't work, or causes mental illness. Medication has a legitimate role in the treatment of many mental illnesses
  3. Medication is the treatment for mental illness. Medication is the ladder that helps you climb out of the hole, therapy is the work of climbing. There is no elevator.
  4. Mental illness is caused by an imbalance of neurotransmitters. This is my favourite misconception. The reality is that we have a very incomplete understanding of most mental illnesses, and neurotransmitter changes may be associative rather than causal. This simplistic misconception is unhelpful at best and self-serving
  5. Mental illness happens to individuals. People live within complex systems of relationships and roles, any understanding or treatment is incomplete without this understanding.
  6. Your past determines your future.
  7. Your past is unimportant. Life experience directly influences brain development, think of it as a type of physical memory rather than a narrative memory. Brain development is plastic throughout life, if it wasn't then we couldn't learn new things and therapy would be unhelpful.
  8. DSM is a universal truth. DSM is only one of many diagnostic systems, but one that is deeply flawed at a conceptual level. That's not to say that diagnoses are unhelpful but they need to be understood with the advantages that any diagnostic system brings, along with it's limitations and flaws.

Is going for a run better for your heart than doing weights inside a gym?

Steady state cardio actually causes your body to pump cortisol into your blood stream which in turn destroys muscle and the heart is entirely an organ-muscle.  Interval style cardio and/or High Intensity Interval Training (HITT) is actually great for your heart because

Have you ever rejected a guy in an arranged marriage because he didn't talk much?

No, I haven't met any groom in arranged marriage setup yet.So, is it a reason to reject a boy because he didn't talk much in first meeting?Think from a boy's perspective, maybe he has just no experience in this kind of meeting.He might be forced to meet you because his parents liked youHe was just feeling a bit

Can I do a week of only core exercises and the next week will be my regular workout routine?

Probably not the best idea to be honest. Regarding whatever goal you have, this would still be a bad idea. Just so you know, it is impossible to localize body fat. It's impossible to lose fat in a certain area. For example, some believe