When you bite off more than you can chew, it means that you have taken on too many tasks or responsibilities. As a result of taking on too much, you may fail at one or more of the tasks you have involved yourself in, and you may also experience high levels of stress and unhappiness. In societies where people are actively encouraged to take on a lot of responsibility, people often bite off more than they can chew, and they may be reluctant to ask for help due to cultural values which frown upon requests for assistance.
Many of us have literally bitten off more than we can chew, and the experience in the metaphorical sense is much the same. In the literal sense, when you but too much food in your mouth, you are often filled with a feeling of panic as you realize that the mouthful is too large. You are forced with the choice of either trying to swallow the mouthful and hoping you don't choke, or spitting it out and starting over again. The choice is much the same in the metaphorical sense.
One of the most common arenas in which people bite off more than they can chew is the workplace. Employees are often encouraged to take on diverse tasks, and they may underestimate the complexity of certain tasks, or overestimate their ability to complete tasks in a timely fashion. When work overloads are combined with a stressful home life, the results can be even worse; single parents, for example, often struggle with finding a balance between home and work.
While it may be tempting to try and forge ahead when you've taken on too much, it is probably advisable to ask for help. Knowing your own limits is very important, especially if you want to become a successful professional. While you may be teased or criticized for asking for assistance, in the end your willingness to recognize the situation will likely play in your favor. Employees who acknowledge the need for assistance are often viewed as more reliable than those who will blindly press on and ultimately make mistakes.
You should also consider the issue of taking on too many responsibilities when you are asked to support charities, participate in extracurricular activities, or make other plans which involve your time or energy. Students especially are prone to flailing as they try to balance social lives, sports teams, schoolwork, and other activities. The stress of handling all of these responsibilities can sometimes undermine the immune system, causing the student to literally become sick from stress.
While you keep an eye on yourself to make sure that you do not bite off more than you can chew, it may be a good idea to also watch out for friends and family members. If someone appears to be struggling but is too proud to ask for help, don't be afraid to step in and assist. It also helps to point out that you know what it's like to be overwhelmed, to establish the fact that you sympathize with the person's struggles.