What is the most difficult to manage stage in a Business Life Cycle, out of the following?

startup, establishment and exit.

Growth, as that's the time one has to ignite all the potentials of the resources available.

GOOD THOUGHT FROM A SMART BRAIN.......... LIKED & APPRECIATED KHATIM,,,,, WELL DEAR SIR,,, EVERY STAGE HAS ITS OWN IF,S & BUT,S ......... BUT AM AGREED WITH ALL HERE THAT IMPORTANT MOST IS THE ........ START UP ,,,, ITS YOUR FIRST IMPRESSION & FACE FOR THE MARKET,,, IF ITS OK & MARKET HAS ACCEPTED YOUR FACE & YOUR PRESENTATION,,, EVERY THING WILL BE FINE IN THE DAYS TO COME........... GOOD DAY

I think the most difficult is to manage the maturity of business.

Startup

(How you cover the various difficulties in the startup stage is more important and rest of the things follow under your control) -its based on my experience please excuse, if the answer is otherwise.

Exit  from business  (in a large organisation)  is also equally difficult to manage, but I didn't come accross such a situation. 

Interesting question, I feel every stage is equally important; the importance depends on type of promoter, for a proprietary concern “seed & startup” is always a challenge, if it’s able to withstand couple of years then the chances are that it would succeed to a great extent.  

“Expansion and Mature” is challenge for established groups of mediocre size; this is the time (even in some cases for big companies) when they become complacent with their achievements, miss out on the fast pace of the market conditions and are over taken by the dynamic & energetic young  companies. It is said that86% of fortune500 companies of1955 have failed and even many companies of the recent origin have collapsed mostly due to overzealous expansion and also due to inaction.  

Any business for that matter is like riding a tiger, you are safe as long as you are alert, and the moment weakness is shown or perceived by the competition, we are gone.

first Startup ... when we get a good start then needs to be maintained for good growth ... 

Groth

Continous growth..

I think the most difficult are how your employees/co-workers react to customers.What is the attitude and how they behave with customers.The way they providing services and responses against their queries. What products you designs or choose for targeted customers. I think these are the most crucial factors.