No matter how secure you feel in your current position, you should never become too comfortable. Things happen: Companies get bought out, some go bankrupt, ownership changes, operations are moved to another country. Or you might simply decide that it's time to move on to greener pastures.

If you want to have the best career possible, and have a successful and happy life, avoid making these five potentially disastrous career mistakes.

1. Burning bridges

Just one unprofessional, disrespectful moment could ruin a career opportunity such as a promotion or new job. A burned bridge is the loss of a potential opportunity. Always treat others with respect and be professional--and stop the gossip chain--whether it is with your peers, the boss, clients, or customers. This applies to social media too. Remember that others will be able to view inappropriate pictures and language use and hit the button labeled Share.

2. Not learning and challenging yourself

If you fall behind the times in knowledge and technology, and stubbornly continue down the old-trusted-ways road, your skills will eventually become out of date or completely obsolete. Instead, continue to learn everything you can about your field, and challenge yourself to take on new projects. Keep up with technology's lightning-fast progress, and keep up with the latest best practices in your field of work.

3. Tossing your résumé aside

So often when we land that great job, the résumé is the first thing to bite the dust in the back of our desk. When the time comes for a job change of any kind, it becomes a very difficult task to polish up the résumé quickly, to remember all the things you have accomplished if you haven't kept a good record. Many people now use LinkedIn or similar sites for keeping an up-to-date record of their positions, progress, achievements, education, and awards. These sites are easy to bring up for your boss to view when asking for a raise or promotion, and they are a great place for a company interested in you to check you out. Keep your résumé current--in an online site or a PDF--and watch the typos and grammatical issues--too many can be a deal killer.

4. Not networking and exploring possibilities

If time and time again you turn down opportunities to attend industry or company events, you are isolating yourself. If you aren't networking and building a base of contacts, how do you expect anyone to know who you are? Be sociable, and meet as many people within your industry and company as possible--there are many people who receive job offers because of whom they know and not necessarily because of what they know. You can also greatly benefit from exploring the possibilities in the job market--find out what other people are doing and how much money they are making in a position similiar to yours. Keeping up on current trends within your field will give you bargaining power as well.

5. Not giving it your all

Completing the bare minimum requirement of work each day, not going above and beyond to help your company or a customer, or not playing nicely on a team is sending the message out to the world--people talk--that you really don't care or are just plain lazy. Make this mistake on an ongoing basis and it could ruin your chance for a stellar career. Here's the bottom line: Be the best you as often as you can, and don't be afraid to take on new challenges or opportunities.