In addition to the key values, XP methodology implementation also requires the support of the three principles of incremental change, embracing change and quality work. Twelve key practices also must be followed: Some traditional methodology practitioners criticize XP as an “unreal” process causing reckless coding. Several traditional software developers find XP inflexible with low functionality and little creative potential. Additional criticisms are that XP: Has no structure. Lacks essential documentation. Has no clear deliverables, i.e., realistic estimates are difficult because the entire project requirement scope is not fully defined. (This lack of detailed requirements makes XP highly prone to scope creep.) Needs cultural change for adoption. (May work for senior developers only) Is costly, i.e., requires frequent communication/meeting at the customer’s expense, which may lead to difficult negotiations. Has possible inefficiency from frequent code changes within various iterations. Of course, as with any development methodology, all this is very subjective and dependant on personal preferences.