What has been the hardest lesson you have learn in procurement/purchasing?

The hardest lesson i have been learn in purchasing how i can select and collect best quality in market .

having single source for critical material

Hardest job is always when you have to purchase an item with unknown manufacturer, brand, or model and the requester provides you with incomplete specs.

if i has an emergency need as well, would be catastrophic ^_^

assuming all aspects prior to shipment has been finalized,  the hardest part is EXPIRY DATE for food, medicines and perishable items and damage for fragile items and quality as common one.

The constitution of the technical committee lies on the hand of other

The procurement principle neglected by other

The application of procurement clause jeopardize your contract

Among the technical committee some member has conflict of interest  

1. Relying on one supplier/ source for critical material and shifting the production plan forward due to unavailability of such material. 

2. End moment non-conformance, due to transit damage.

3. Missing of a particular component, which may cause the disturbance in a manufacturing process.

4. Getting non-conformance reports from our internal QA/QC department, upon goods arrival. 

I have experieced too many hardship when it comes to purchasing such as material specifications, payment terms to be used, minimum cost with best quality, dealing with suppliers, type of incoterms to be used etc.  But the hardest lesson i have been learn in purchasing is to ensure that all long lead items, you should always put Liquidated Damages and ask for whatever bonds for the safety of your side.

My Business specialization in the export of fresh fruits and vegetables

And my lesson is a difficult balancing quantities and quality for agricultural crops

Simply, How can I find best price, quality in no time with no risk !?

delaying in the lead time of some orders and customs holidays and  logistics problems of missing  cartons (LCL) shipmants especially for back to back orders

Don't depend only on the Foreign Suppliers. May be some times shipments will stuck in the port due to customs or any other issues. If the material not reach to the plant on time then it will be a huge problem. So always secure the healthy stocks and always maintain the relation with the local suppliers who can deliver you the same quality in this critical situation