"Her failure was a useful preliminary to success."
Undine appears to be the kind of woman who will stop at nothing to get what she wants. To her, failure is merely a trial run. She is tenacious, but also lacks certain ethical standards which would help her to learn how to be more successful the first time. Unfortunately this flippant attitude toward failure, which may be helpful to a small business owner, is less desirable when considering marriage and divorce. Her relationship to failure and success continues to remain steadfast even as Undine slips through several marriages.
"She had everything she wanted, but she still felt, at times, that there were other things she might want if she knew about them."
In this excerpt we see Undine's true flaw revealed; she has confused desire with satisfaction. Unable to silence her anxieties, Undine has allowed herself to believe that material possessions and reputation will bring her happiness. While everyone is looking to be happy, Undine decides that her happiness is entirely dependent upon circumstances, which makes her a very undesirable companion.
"The turnings of life seldom show a sign-post; or rather, though the sign is always there, it is usually placed some distance back, like the notices that give warning of a bad hill or a level railway-crossing."
Undine finds herself only just starting to establish herself late in life because she's spent so much of her time seeking happiness but never committing to any one path to getting there. She's quickly abandoned relationships and lifestyles, one after the other, so that by the time she looks up she sees all of her peers nicely settled in and enjoying the benefits of old age, while she still has nothing to show for herself.
"Just so; she'd even feel aggrieved. But why? Because it's against the custom of the country. And whose fault is that? The man's again -- I don't mean Ralph I mean the genus he belongs to; homo sapiens, Americanus. Why haven't we taught our women to take interest in our work? Simply because we don't take enough interest in THEM."
Undine is unable to marry Raymond de Chelles because she has been divorced from Ralph, and divorce is against his religion as a Catholic. The two commiserate together and decide that really it is society's fault that so many people end up unhappy. If other people's -- men's -- standards had not been so rigid and judgmental, then these two could be happy right now.