A habit (or wont) is a routine of behavior that is repeated regularly and tends to occur unconsciously. In the American Journal of Psychology (1903) it is defined in this way: "A habit, from the standpoint of psychology, is a more or less fixed way of thinking, willing, or feeling acquired through previous repetition of a mental experience." Habitual behavior often goes unnoticed in persons exhibiting it, because a person does not need to engage in self-analysis when undertaking routine tasks. Habits are sometimes compulsory. The process by which new behaviours become automatic is habit formation. Old habits are hard to break and new habits are hard to form because the behavioural patterns we repeat are imprinted in our neural pathways, but it is possible to form new habits through repetition.
As behaviors are repeated in a consistent context, there is an incremental increase in the link between the context and the action. This increases the automaticity of the behavior in that context. Features of an automatic behavior are all or some of: efficiency, lack of awareness, unintentionality, uncontrollability.
Habit formation is the process by which a behaviour, through regular repetition, becomes automatic or habitual. This is modelled as an increase in automaticity with number of repetitions up to an asymptote. This process of habit formation can be slow. Lally et al. (2010) found the average time for participants to reach the asymptote of automaticity was 66 days with a range of 18–254 days.
As the habit is forming, it can be analysed in three parts: the cue, the behavior, and the reward. The cue is the thing that causes your habit to come about, the trigger to your habitual behaviour. This could be anything that your mind associates with that habit and you will automatically let a habit come to the surface. The behavior is the actual habit that you are exhibiting and the reward, a positive feeling, therefore continues the “habit loop.” A habit may initially be triggered by a goal, but over time that goal becomes less necessary and the habit becomes more automatic.
Habits and goals
The habit–goal interface or interaction is constrained by the particular manner in which habits are learned and represented in memory. Specifically, the associative learning underlying habits is characterized by the slow, incremental accrual of information over time in procedural memory. Habits can either benefit or hurt the goals a person sets for themselves.
Goals guide habits by providing the initial outcome-oriented motivation for response repetition. In this sense, habits are often a trace of past goal pursuit. Although, when a habit forces one action, but a conscious goal pushes for another action, an oppositional context occurs. When the habit prevails over the conscious goal, a capture error has taken place.
Behavior prediction is also derived from goals. Behavior prediction is to acknowledge the likelihood that a habit will form, but in order to form that habit, a goal must have been initially present. The influence of goals on habits is what makes a habit different from other automatic processes in the mind. Habits as described by animal behavior experiments were investigated in "A series of elegant experiments  conducted by Anthony Dickinson and colleagues in the early 1980s at the University of Cambridge in England".
Habits and nervousness
There are a number of habits possessed by individuals that can be classified as nervous habits. These include nail-biting, stammering, sniffling, and banging the head. They are known as symptoms of an emotional state and are generally based upon conditions of anxiety, insecurity, inferiority and tension. These habits are often formed at a young age and may be because of a need for attention. When trying to overcome a nervous habit it is important to resolve the cause of the nervous feeling rather than the symptom which is a habit itself 
A bad habit is an undesirable behavior pattern. Common examples include: procrastination, fidgeting, overspending, nail-biting. The sooner one recognizes these bad habits, the easier it is to fix them.
Will and intention
A key factor in distinguishing a bad habit from an addiction or mental disease is willpower. If a person has control over the behavior, then it is a habit. Good intentions can override the negative effect of bad habits, but their effect seems to be independent and additive—the bad habits remain, but are subdued rather than cancelled.
Eliminating bad habits
Many techniques exist for removing established bad habits, e.g., withdrawal of reinforcers—identifying and removing factors that trigger and reinforce the habit. The basal ganglia appears to remember the context that triggers a habit, so habits can be revived if triggers reappear. Recognizing and eliminating bad habits as soon as possible is advised. Habit elimination becomes more difficult with age because repetitions reinforce habits cumulatively over the lifespan. According to Charles Duhigg, there is a loop that includes a cue, routine and reward for every habit. An example of a habit loop is TV program ends(cue), go to the fridge(routine), eat a snack(reward). The key to changing habits is to identify your cue and modify your routine and reward.
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- Arthur Payne,(n.d) The psychology of nervous habits
- James Rowland Angell and Addison W. Moore. (1896) "Studies from the Psychological Laboratory of the University of Chicago: 1. Reaction-Time: A Study in Attention and Habit." Psychological Review 3, 245–258.