Key factor is nothing but a limiting factor or deterring factor on sales volume, production, labour, materials and so on.
The limiting factor normally differs from one to another
Volume of sales- the limiting factor is that production of required number of articles
Volume of production- the limiting factors are as follows in adequate supply of raw materials, labor, and inability to sell the produced articles and so on
The limiting factors are studied in the lights of the contribution. The limiting factor is bearing the inverse relationship with the volume of contribution. To study the worth of the business proposals among the limiting factors, the contribution is considered as a parameter to rank them one after another.