Behaviour is a function of and determined by the environment, learning and current conditions; personality is the collective term. Weather is to climate like behaviour is to personality.
The structural (most common) approach to personality is that traits remain stable across time and behaviour is a function of those traits. Behaviourism is a functional approach; personality is descriptive (it describes the collection of behaviours that are stable over time). So instead of personality (stable-ish) > behaviours, it’s behaviours (stable-ish) = ‘personality’.
A personality trait is thus a hypothetical construct inferred from past behaviour. They do not help explain certain behaviours. A hypothetical construct, e.g. depression, cannot be measured directly, but through its effects i.e. future behaviour(s) such as decreased activity. Behaviourists however look at someone’s history to figure out the cause(s) of the hypothetical construct and the caused behaviour, which might be the person having been abused as kid.
Behaviours are learnt through a) classical conditioning (motivation) or b) operant conditioning (consequences).
Impulsiveness is an operant behaviour (consequences influence behaviour in choice situations). People with low self control tend to go for ‘small’ but ‘soon’ rather than ‘long’ but ‘better’ (adjusted delay vs fixed delay). A typical (test) situation would be when you’re presented with a small biscuit and you’re told that you can have it now, or wait another 20 minutes and get a second one. People discount (change the value of consequences), which is the underlying difference between self-control and no-self control.