It does not come automatically, simply because one is a worker. The historic path to a united, integrated working class has been marked by many obstacles, many setbacks and advances. Such a process is slow because it is fundamentally a process of development of a class ideology and a class outlook.
Ideology is the result of experience built upon experience.
There are three basic levels and qualities of working class unity. Unity around economic struggles like jobs, wages and working conditions is the first level of unity. No strike can be won without this most basic level of unity. In a sharp class struggle like a strike, workers know who the enemy is. There is no room for neutrals or sitting on the sidelines out of the battle zone.