Fear of Unknown has played some parts in hindering progress, development or taking a firm decision in life. Many had brushed it aside and regret it while some had cause to smile to taking the risk. (talk of the devil you known is better than the angel you don't know).
For instance:
you are in a job and you are not comfortable for one reason or the other and you are contemplating leaving to find another job but you are cautious and held back for the fear of unknown - Will I get another job easily? Will my new boss or job be worse than the current one.
You are dating a potential marriage partner for a while and you seem to know everything about him/her but you are eyeing another person and you are like will he/she be better? what if I later ended up jumping from frying pan to fire?
Personal example, I was in a job where I don't like the attitude of my boss and working conditions but I had to endure it for several years for the fear of not getting a job or getting a worse job. After several years and when I couldn't bear it anymore, I left for another and today, I am regretting leaving that job because even though the working condition was better my boss was hell compared to my last job.
This fear of unknown has been positive to some while reverse is the case for others
What is your experience on 'fear of unknown'