This study is dedicated to the reinvestigation of the role of the particle lɛɛw45 in Thai. It raises speculations over the conventional claims according to which lɛɛw45 plays a role in temporality as a perfective aspect marker (Kanchanawan, 1978; Boonyapatipark, 1983; among others). The reappraisal of the role of lɛɛw45 in this study, which is based on the use of it in present day Thai, offers an argument against these claims. The addition of lɛɛw45 to a sentence is not mainly aimed at temporal effects. When it appears in a sentence, lɛɛw45 does not necessarily denote the perfective aspect of the event. Moreover, it can be omitted in the sentence in which perfectivity is already inherited through the lexical aspect of the verb and the temporal structure of the predicate. Lɛɛw45 in fact plays a role as a marker of counter-expectation. It represents a previous expectation about the subject and its opposition to the asserted proposition. Examining the nature of lɛɛw45's implications thoroughly, the study has found that even though the definiteness of the subject behaves like a standard presupposition, the implicated expectation does not project in all cases. This is revealed in the results from Tonhauser et al.’s (2013) projection tests. Lɛɛw45 is context-sensitive and imposes a Strong Contextual Felicity constraint. Nonetheless, it is actually not bound to Obligatory Local Effect and its presence in the context where the projective contents are not entailed is also felicitous. Counter-expectations also involve coherence and relevance, which are determined by the interrelationship between common ground, context, and focus. The asserted proposition is required to correspond to the common ground knowledge and context designated by the expected proposition. Additionally, the expression and interpretation of lɛɛw45's counter-expectations rely on the association of lɛɛw45 with the focused element in its scope. In a particular case, the common ground knowledge, context, and focus can be identified with the assistance of Question Under Discussion (Roberts 1996, 2012). The mechanism also accounts for the production and interpretation processes proceeding in accordance with the conversational moves.