Its is cause by mostly 2 reasons > 1. Fear Let me clear our brain cannot distinguish between life threatening situation and simple easy daily life non - threatening situation I.e ( public speaking , bcoz we are social being and its important Let me clear our brain cannot distinguish between life threatening situation and simple easy daily life non - threatening situation I.e ( public speaking , bcoz we are social being and its important for us to make an good impression on society that's where fear and anxiety arise ,bcoz its is important ). You become socially anxious and then when you get chance to speak your brain will initialize the fear and stress response , and even people who are fluent tends to stutter or get freeze during a stressful situation , not just speech your whole body get tight as if ready to fight or flight ( run ) or freeze . fear and stress response , and even people who are fluent tends to stutter or get freeze during a stressful situation , not just speech your whole body get tight as if ready to fight or flight ( run ) or freeze . > 2. Pressure of fluency . Fluency doesn't require force or anything it comes by its own , it has its own flow ( like when you try to create humour in order to become interesting person , but humour cannot be forced or created by just thinking , it comes by its own and its has its own flow ) but when you try to become fluent your brain try to help you by adding extra force as if to force out word but , this is response of brain in pressure , fear or of doing task that is important ( like proposing to your love partner or talking to your boss ) . This response is helpfull when you do a physical task like running , fighting or some physical task But it acts totally oppositely in situation when you need to focus , when you need precision ( singing ) , delicate task like making paintings . So , that's why singer practise like a singer and when they go on to the stage they behave and think like they are not singers that help to reduce pressure . Don't judge yourself or let others judgement affects you ,and before going into speaking situation always be positive and aware of your thought and body , and in the middle of situation just ie middle of block , don't force or feel pressure just stop let that block dissolve and DON'T TRY TO SPEAK or THINK Of Speaking bcoz our brain has built shortcut bcoz ie speaking => danger (getting stuck , humiliation ) => Forcing and uncontrollably faster movement speaking habits => avoid , run or to overtly stutter . But over times our brain create shortcuts that speaking => () => avoid or overtly stutter . SO thats why DON'T TRY TO SPEAK or THINK Of Speaking bcoz our brain has built shortcut .