This is a great question and one of which where either you have an identical twin somewhere else whom is in the exact same situation as you or your looking to validate something you already know to be true.
The insecurity can be more of a personal issue; for example, do you fear change? have anxiety and so on? Do you have bills to pay? blah blah blah. If you have this, then change unless forced will be very difficult and even if you change jobs, you may suffer from what I like to call the "new car syndrome" (also applies to girl friends/partners too). You get a new car, you like it, but you always like the old one more.
If you are one or more of the following:
Unhappy at your current job
Learning has become stagnant
Career advancement or track changes are not possible
Management doesn't offer assistance to learn new things
Then you probably have a great reason to leave your current employment, but before you do so - have you:
Spoken to management?
Had a review where you could talk about objectives and performance?
Looked into further training in which your employers may be able to assist you?
Often employers or management are unaware that their workers are having these issues (and often personal issues) unless they themselves are made aware directly through you talking to them!