What is the secret of success of SAP?

SAP is a visionary company that could visualize the emergence of ERP twenty years back. Its flagship product R/3 also capitalized the client-server technology in late 80's, which was the right time to leverage client-server technology for mission critical applications.
Many leading companies such as Microsoft in software, Intel in microprocessor, IBM, HP, Compaq & Digital (today only Compaq) in computer industry are with SAP.